ActiveDay

Calorie Calculator

Estimate your maintenance calories (TDEE) from your stats and activity level, with ready-made targets for losing or gaining weight.

Fill in all fields to see your maintenance calories.

What this calculator does

Every plan to lose, gain, or hold weight starts from one number: how many calories your body uses in a normal day. This calculator estimates that number — your total daily energy expenditure, or TDEE — in two steps. First it computes your basal metabolic rate (BMR) with the Mifflin-St Jeor equation, the formula the American Dietetic Association found most reliable for healthy adults. Then it multiplies BMR by an activity factor that accounts for your training and daily movement.

Eat near your TDEE and your weight holds steady. Eat consistently below it and you lose weight; consistently above it and you gain. Every diet that works — keto, fasting, plain portion control — works through this mechanism.

The formula

Men

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5

Women

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

The activity multipliers range from 1.2 for a sedentary lifestyle to 1.9 for a physical job combined with hard training. Most people who train a few times a week but sit for work belong in the 1.375–1.55 range. If in doubt, pick the lower option — overestimating activity is the most common way calorie targets end up too high.

Choosing a target

  • Losing weight: subtract roughly 500 kcal from TDEE for about 0.5 kg per week. Keep protein high — see the protein intake calculator — so the weight you lose is mostly fat.
  • Maintaining: eat at TDEE and watch the weekly average of your weight, not single weigh-ins.
  • Gaining muscle: add 200–300 kcal. Bigger surpluses speed up fat gain far more than muscle gain.

Whatever the target, split it into macros next — the macro calculator turns a calorie number into protein, carbs, and fat.

Why estimates need adjusting

Two people with identical stats can differ by a few hundred calories a day in real expenditure, mostly through fidgeting and non-exercise movement. So treat the calculator as your starting line: eat at the suggested target for two to three weeks while logging honestly, compare your average weekly weight, and nudge intake by 100–200 kcal if the trend is off. That feedback loop — target, track, adjust — beats any formula on its own, and it is exactly what ActiveDay automates: log meals with the AI food camera or barcode scanner, let workouts sync from Apple Health, and read the weekly trend instead of guessing.

Frequently asked questions

  • How accurate is a calorie calculator?

    Equations like Mifflin-St Jeor are accurate to within roughly 10 percent for most people, but individual metabolism, daily movement, and logging accuracy all vary. Treat the result as a starting point, track your weight for two to three weeks, and adjust by 100 to 200 kcal if the trend does not match your goal.

  • What is the difference between BMR and TDEE?

    BMR is the energy your body burns at complete rest. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor to account for movement, exercise, and digestion. TDEE is the number to eat against.

  • How big should my calorie deficit be?

    A deficit of about 500 kcal per day produces roughly 0.5 kg of weight loss per week, which is sustainable for most people. Larger deficits work faster but cost more muscle, energy, and adherence.

  • Should I eat back exercise calories?

    If you chose an activity level that already includes your training, no — they are counted. Only add calories for exercise that goes clearly beyond the activity level you selected.

  • Why am I not losing weight in a calorie deficit?

    The most common reason is that the deficit only exists on paper: untracked snacks, oils, and weekend meals close the gap. Water retention can also mask fat loss for weeks. Tighten logging first, then reduce intake slightly if four weeks pass without trend movement.

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